Smashing mantis shrimp strategically impact shells

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Crane, R.L., S.M. Cox, S.A. Kisare, and S. N. Patek. 2018.  Smashing mantis shrimp strategically impact shells. Journal of Experimental Biology 221, jeb176099DOI:10.1242/jeb.176099.

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Journal of Experimental Biology

The ability to break canonically strong mollusk shells is a key strategy for many predators, often requiring specialized weaponry and behaviors. Current understanding of shell fracture mechanics is primarily based on relatively slow application of forces (high impulse, low peak force), mimicking jaw and claw-based predators, whereas the principles underlying the biomechanics and behavioral strategies of impact fracture (low impulse, high peak force) remain uncertain. We measured how mantis shrimp (Neogonodactylus bredini) break snail shells and tested whether they strike shells in different locations depending on prey shape (Nerita spp., Cenchritis muricatus,Cerithium spp.). Using a physical model of mantis shrimp, we tested whether certain strike locations are particularly effective for fracturing shells. We found that, contrary to their formidable reputation, mantis shrimp often required tens to hundreds of strikes to open a shell. They targeted distinct impact locations depending on shell type, consistently striking the aperture of low-spired shells and alternating strike location from aperture to apex in high-spired shells. Tests using a physical model (Ninjabot) revealed that mantis shrimp avoid striking regions that cause little damage. Mantis shrimp target specific shell regions and alter their strategy depending on shell shape. We provide a first window into the mechanical and behavioral strategies underlying the successful use of the fast-accelerating and lightweight mantis shrimp hammer. The integration of naturally variable experiments of mantis shrimp strike behavior alongside the use of controlled tests using Ninjabot enabled insights into shell impact fracture, an area of biology in need of a foundational framework.

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